Conventional chip manufacturing is divided into front-end, back-end, and tail-end processing. Front-end of the line (FEOL) processing refers to the fabrication of transistors, while back-end of the line (BEOL) processing describes wafer metallization. Tail-end of the line (TEOL) processing refers to the packaging of the individual dice. Generally, the final wafer-level process step is the fabrication of vias through a passivation layer to expose the die pads, which serve as the interface between the die and the package. Each individual die, while still part of the wafer, is then functionally tested to identify known good die (KGD) followed by wafer singulation. The KGDs are then shipped to a packaging foundry where they are individually placed in a temporary package for burn-in. The dice that pass this test are then individually packaged into their final package and tested again for functionality. This final step concludes tail-end processing and the functional packaged dice are finally ready for system assembly.
The mechanical performance of a package is important for wafer-level testing, protection, and reliability. Wafer-level testing of electrical devices requires simultaneous reliable electrical contact across a surface area. Typically, neither the wafer nor the testing substrate is planar enough to enable this reliable temporary electrical contact. In-plane (i.e., x-y axis) compliance is generally required to account for potential problems such as, for example, thermal expansion mismatch between the chip and printed wiring board and probe contact with leads. Wafer-level testing and burn-in demand significant out-of-plane plane (i.e., z-axis) compliance in order to establish reliable electrical contact between the pads on the non-planar wafer and pads/probes on the board surfaces. Non-compliance of the input/output (I/O) interconnects/pads out-of-plane, as well as in-plane (i.e., x-y axis), can cause difficulties in performing wafer-level testing. For optical interconnection, the alignment between the chip and the board should be maintained during field service to minimize optical losses due to offset.
A key interconnection level that will be severely challenged by gigascale integration (GSI) is the chip-to-module interconnection that integrates the packaged chip into the system. A gigascale system-on-a-chip (SoC) demands the development of new and cost effective integrated input/output (I/O) interconnect solutions that use high-performance integrated electrical, optical, and radio frequency (RF) approaches to meet all of the I/O requirements of the 45 to 22 nm International Technology Roadmap for Semiconductors (ITRS) technology nodes (International Technology Roadmap for Semiconductors (ITRS), 2002 update, SIA). Meeting these challenges is essential for the semiconductor industry to transcend known limits on interconnects that would otherwise decelerate or halt the historical rate of progress toward GSI and beyond. In general, power, clock, and signal I/O functions will be met by the selective integration of fine pitch electrical (<30 μm pitch area array), optical, and RF I/O interconnect technologies. These high-density integrated I/O interconnects will be especially important for novel 3D structures as well as for high current (>400A) and high bandwidth (>40 Tbs) applications. To investigate the above issues, focus should be given to overcoming long-range and fundamental barriers in chip-to-module interconnects by advancing fine-pitch compliant interconnections, optoelectronic and RF interconnections, and wafer-level testing and burn-in.
Accordingly, there is a need in the industry to address the aforementioned deficiencies and/or inadequacies.